1. Field of Invention
The present inventions relate to designing and operating canal locks to lift and lower vessels, with emphasis on reducing per-transit water-use.
2. Description of Prior Art
A lock is a water-containment chamber—with sealing gates at each end—installed between a lower and an upper waterway. Water is either added to or removed from the chamber to respectively lift or lower the vessel or vessels floating in it. While the engineering, materials and construction of a lock's main components—its chambers, gates, pipes and valves—have notably improved over the millennia, it is still preferable to use gravity to move the water in and out of the lock chambers. Gravity flow has traditionally been preferred over pumping for reasons of efficiency and reliability, as pumps require power to run them and are a source for failure.
At the Panama Canal water is drained in and out of each chamber tens of times a day following 100-year-old procedures, demonstrating the reliability of gravity-operated locks. At that canal, a series of gravity-operated locks raise ships arriving from one sea three steps to the level of a lake; after they traverse the canal's lakes and channels across the Isthmus, they are lowered three steps to the other sea by another series of such locks.
The original three-step Panama Canal locks as traditionally operated expend about 98,500 cubic meters (26 million gallons) of Gatún Lake water to raise a transiting ship; and, they use the same again to lower it. For 2003, there were on average 38 transits a day that year; thus, about 7.5 million cubic meters (2 billion gallons) of lake water were used each day. Had the original Panama Canal lock system had only two steps, half-again more water would have been required to transit a ship than what is typically used today. Conversely, had there been four steps, only three-quarters of the water used today would have been needed. Thus, how much water a set of gravity locks uses is strongly tied to its number of steps. However, deciding how many steps to use is best determined by assessing other approaches for reducing water-use, such as recycling, modifying lock layouts and using alternative sequencing of transits. For a lock canal to be successful, a reasonable balance between transits and water-use must be found.
Water to operate the Panama Canal comes from rain. During the tropical rainy season, the present Panama Canal typically receives sufficient water to permit the highest throughput of ships. Only about half the water that falls in the canal's watershed during the rainy season ends up used to lift or lower ships due to storage capacity limitations; some of the excess water is used to generate power, but much goes out to sea unused. Panama Canal transit operations have been curtailed at least once when water was in short supply due to reduced rainfall, which was costly to shippers. Madden Dam (on the Chagres River, above the Canal's main waterway) was added a few decades after the Canal was built to augment the system's water-storage capacity. Nonetheless, water-reserves did fall short fairly recently, validating calls for more improvements to be made. Adding more water-storage capacity to the Panama Canal has been contemplated for decades since Madden Dam was added, still no new dams with reservoirs have been built. Yet, increasing water reserves and devising methods to reduce water-use, continue to be goals for the Canal to assure the system's reliability as demands for service grow.
In addition to time and water-availability constraints that limit the amount of cargo that can be transited, two other present Panama Canal limitations that impact both world shipping and Panama's revenues are that: 1) ships larger than Panamax Class can't transit and 2) canal transits are sharply reduced when locks get overhauled. (“Panamax Class” ships are the largest that physically fit inside the original Panama Canal Locks). To provide larger ships a shorter, more cost effective travel route and to gain revenue from transiting them, adding a larger lane to the Panama Canal has been contemplated for several decades. Having more capacity would also lessen the relative impact to the Canal's revenue stream caused by the periodic overhauls of its locks.
An effort to add a new lane to the Panama Canal is presently underway. Plans are to add side-tank locks of the previous art, with chambers larger than those of the Canal's original locks and which have a water recycling capability. Those locks are to have three tanks parallel to and to one side of each chamber, to and from which water is to be transferred, or recycled, to reduce the system's per-transit water-use; the planned locks will use about 40% of the volume of water a traditionally configured and operated lock uses. For reference, if those side-tank locks were to have two (instead of three) tanks beside each chamber, the per-transit water-use of those locks would be about 50%. With one tank per chamber, water-use would be about 66.7% of a traditionally operated lock.
The method of using such “side-tanks” to reduce lock water-use was introduced several decades before the Panama Canal was built. When the original Panama Canal locks were built, their design included another water-recycling method then available.
Without tanks, that other water-recycling method can reduce the water used per transit of the two-lane Panama Canal lock system to about half of what is traditionally used; the Panama Canal's designers intended for that method to be used during the dry-season. Per that method, half the water drained from a first chamber when lowering its level is directed laterally into the adjacent lane's chamber to begin raising its level; then, only the lower half of the water in the first chamber drains out to the lower waterway and only half the water to fill the adjacent second chamber needs to be drained in from the upper waterway. However, other than tests of the method having been done under the Canal's US Administration, the method wasn't used, as shipping demands apparently did not exceed the system's water reserves with Madden Dam added. Fewer transits and less revenue would have resulted from taking time to save water, only to dump it for lack of storage capacity.
The most critical element of a canal is its ship-lifting system. The lifting device chosen should not only maximize transits for the cost of its construction, but it should minimize the system's overall cost. Beyond the direct costs of design and construction, indirect costs to canal neighbors and to the environment that are generated during and subsequent to the construction effort must be quantified and taken into account.
The concern with the expansion of the Panama Canal is that the plan will add a relatively high-cost, low-return system that will cause excessive and unnecessary impact to third parties and to the environment ad infinitum. That concern prompted the undertaking of an independent investigation of ship lifting systems with the intent of determining whether or not improvements to available technologies could be made.
Mechanical ship lifts were investigated at the outset. That work resulted in the development and patenting of a new mechanical lift capable of handling the world's largest ships, as disclosed in my U.S. Pat. No. 7,354,223.
The assessment of locks that followed has resulted in the development of the new, more efficient lock design and canal operating methods claimed in this document.